The protest comes after reports that work is underway in secret at Britain’s nuclear bomb factory to upgrade the existing Trident arsenal and to develop an entirely new warhead.

The AWE at Aldermaston and Burghfield in Berkshire is working on a programme to upgrade the current UK Trident warhead to produce the “Mark 4A”, which will be more accurate and have greater destructive power, according to a report by the Nuclear Information Service. The costs and timetable of the programme have not been revealed to parliament.

As British activists continued with the action at Burghfield – which involves participants forming chains by locking their arms together inside tubes – they were joined on Wednesday by others from Belgium, France, Germany and Finland.

The group described the direction action at the 225-acre site as the longest continuous blockade of a nuclear weapons facility.

“We don’t know why they haven’t moved us but we are quite happy with that,” said Angie Zelter, one of the founders of Trident Ploughshares. “It’s the first time that we have ever been able to do anything like this.” She added that she had been told by the police that construction work at the site had come to a halt because of the action.

Between 20 and 30 people were involved at any one time in the blockade, she said, including an 87-year-old who lay down on the roadway and another man who was in a wheelchair.

Thames Valley police said on Wednesday that four people had been charged in connection with the obstruction of a roadway near Burghfield on Tuesday. The four – who were aged 18, 25, 32 and 62 – were released on bail to attend Reading magistrates court later in June.